This application claims the priority of European application 00114618.2, filed Jul. 7, 2001, the disclosure of which is expressly incorporated by reference herein.
The invention relates to condensing heat exchangers, and more particularly to condensing heat exchangers employing both a condenser section and a slurper section.
A condensing heat exchanger is a main component of air conditioning systems. It simultaneously cools and de-humidifies the air to be conditioned. During this process water condenses on the surface of the air side surface (air fins) of the condensing heat exchanger. The condensed water on the air fins has to be separated from the air stream. On earth this is generally done by the gravity forces. For space applications under the absence of gravity the condensed water is sucked off by applying underpressure.
A prior art design principle (FIG. 1) already proven in several applications, e.g. in spacelab missions, is to add a so called slurper section 3 to the condenser section 1 of the condensing heat exchanger 16 from which the condensed water together with some air is sucked off through the slurpor holes 7 by applying underpressure. However, this design requires that the air flow velocity is high enough to push the condensed water out from the air fins against the capillary forces which tend to hold the water inside the air fins. In case of low air flow velocities and when the distance between neighbouring fins 2 is small a significant amount of water can accumulate inside the air fins and is released spontaneously. This could result in a poor water separation performance of the slurper section.
The object of the present invention is to provide a condensing heat exchanger in which trapping of the condensate inside the condensing section can be decreased and a high water separation can be obtained.
In accordance with the invention the condensing heat exchanger comprises a capillary bridge, which connects the condensing section and the slurper section of the condensing heat exchanger. The capillary bridge comprises capillary spaces wherein the condensate formed on the fins of the condenser section is transported inside the slurper section by means of capillary forces.
In a preferred embodiment the capillary space is defined by an interstitial space which is formed by at least one plate arranged in proximity to a section of the internal surface of the slurper section. The water is pulled from the condensing section into the interstitial spaces between the plates and the surface of the slurper section by capillary forces and transported inside the slurper section. By applying, for example, reduced pressure the water together with an air stream penetrates through dedicated slurper holes through which it exits the slurper section.
The plates can be attached to the surface of the slurper section by means of clamps or bolts. An advantage arising from the use of clamps or bolts for attaching the plates to the slurper section is that the capillary bridge is capable of being added to an existing hardware or being removed after assembly of the condensing heat exchanger.
In another embodiment of the invention the capillary bridge is formed by a capillary fleece or mesh. The water is pulled by capillary forces from the air fins into the cavities of the fleece or mesh and then exits by applying e.g. reduced pressure together with an air stream through dedicated slurper holes.
In the case of the capillary bridge comprising plates, the distance between the plates and the internal surface of the slurper section, which affects the capillary force, is adjusted by dedicated spacers. When using a fleece or a mesh as capillary bridge the fleece or mesh is directly applied on the internal surface of the slurper section without spacers. The plate, fleece or mesh can be attached by mechanical treatments e.g. solding or welding.
In a further embodiment of the invention the surface of the condensing section is coated. Preferably a hydrophilic coating is used. Thus, the transport of the water condensed on the air fins toward the capillary bridge is supported. Other surface treatments, e.g. mechanical, thermal or chemical treatments, which result into a hydrophilic characteristic of the surface are possible.
The condensing heat exchanger according to the invention can be used under microgravity conditions or under 1 and higher gravity conditions. In the case of using the condensing heat exchanger under micro-gravity conditions, e.g. space applications, the water is extracted from the air stream in the slurper section through applied underpressure. In this application the condensing heat exchanger can be used in any spatial orientation.
When the condensate should be removed solely by gravity, for example, on earth, the condensing heat exchanger should be oriented in such a manner that the plates forming the capillary bridge are oriented parallel to the gravity force. The water sucked into the capillary bridge by capillary forces is pulled down to the bottom of the capillary bridge by gravity. At the bottom of the capillary bridge a water column is formed. If the height of the water column in the capillary bridge produces a hydrostatic pressure which is greater than the capillary pressure of the capillary bridge the water can leave the capillary bridge. In order not to block the water suction from the fins at the bottom of the condenser section the slurper section including the capillary bridge has to be extended below the bottom of the condensing heat exchanger. So it is guaranteed that the water can leave the slurper section by gravity forces without applying underpressure.
The present invention is dedicated mainly to space application for use in manned spacecrafts. However, it can also be applied on earth to improve water separation performance of a condensing heat exchanger.